I REALLY HOPE SOMEONE CAN HELP ME

First, I?™m novice and this is my first time posting for help in a forum.  So, forgive my ignorance.  

I attached 2 links to short slow motion videos of the Dr. Debug cycles the machine provides.  When I have a barebones setup with 1 RAM module in A1 or A2, the machine ends the POST at code C0.  Then recycles and repeats seemingly indefinitely.  When I have 4 RAM modules in A2, B2, C2 and D2 (as the manual directs) the machine makes it farther through what I think is the POST process, but ends on Dr. Debug code 90.  It does not recycle as it does with 1 RAM module.  

https://drive.google.com/file/d/1QTp9yOPFU1RmmzGYhwCzbQq96rV_0oGH/view?usp=sharing

https://drive.google.com/file/d/1yj_RU4VxKTQ3PRnBvVaM2sGlad2PBbcQ/view?usp=sharing

Upon powering up, PC lights up and begins, CPU Cooler fan spins every time and it begins what appears to be the POST cycle.  Then it stops/ends and remains on Dr. Debug code 90 (the MB does not make any beep and I have no speaker connected).

I?™ve tried the following recommendations (and others not listed) with no success:  After unplugging PSU, clearing CMOS and upon power up, the MB RGB (under the gear near the chipset) consistently flashes 5 times and then begins the slower ?œbreathing??flashing.  I?™ve unplugged, cleared the CMOS and removed components individually, then reconnected PSU and powered up.  Sequentially, I?™ve removed CAT 6 connection, GPU, M.2 SSD, SSD, Keyboard and mouse, then RAM.  Then I repeated this leaving the GPU connected in hopes of getting the monitor to register a signal - to no avail.  I have tried 3 different electrical outlets and am on a functioning 20 amp breaker with no other appliances or power draws.  I?™ve removed power strip, extension cord, Kill A Watt, plugged directly into the wall, but no success or variation - Dr. Debug code 90 every time.  I even unhooked the MB?™s 4-pin 12V power connector . . . same result.

Exception - Upon unplugging PSU, removing ALL RAM and components (except CPU and Cooler), clearing CMOS, reconnecting PSU and powering up, PC began POST cycle and ended with Dr. Debug code C0.  This is the only variation I?™ve obtained.

I?™ve tried getting the PC to POST well over 200 times.  I?™ve disassembled, cleaned and reassembled the system twice (I scanned socket each time for bent pins but saw none).  Working to be methodical, I unplugged PSU, removed one component at a time, reconnected PSU and powered up.

I feel dumb, I?™m beyond Amazon?™s return window and tech support windows.  Also, this MB has USB Type C video out and I do not have that cable.  I thought it strange that I?™ve never gotten the monitor to recognize the MB, GPU nor register receiving a signal.  The monitor has Display ports, Mini Display Ports, HDMI, and USB.  I?™ve tried them all and am unsure how to connect the MB to the monitor, thus I?™ve relied on the GPU and no monitor w/ Dr. Debug codes.

I?™ve photographed the build and made a slow motion video of the PC going through POST cycle with Dr. Debug.  If I can provide any other info that would help you help me, I?™ll happily oblige.

Any guidance, suggestions or ideas are much appreciated.

Openair build on extruded  aluminum w/ 5mm brass standoffs (I do not have any headers connected nor speakers)

PSU: Corsair AX1500i 

MB:         ASRock X399 Taichi

BIOS: 2.00 (sticker on BIOS chip)

CPU: AMD Ryzen 1950X

Cooler:         Noctua NH-U14S

RAM: 8GB X 4 G.Skill FlareX F4-3200C14Q-32GFX DDR4

GPU: 2X AMD Radeon Vega Frontier Edition

STORAGE: Samsung V-NAND SSD 850 EVO; NOT INSTALLED 2X WD Blue 3D NAND SSD M.2 2280

MONITOR: Dell S2817Q

KEYBOARD: Hermes E1

MOUSE:         Hermes E1

OPTICAL: LG SP80

OS:         None installed but I have the Windows 10 Pro CD that I plan to install if I can get through POST and then BIOS configured